These days it seems our entire way of life is predicated on the belief that being overweight is terrible for you. We're waging war against the obesity epidemic, which public health experts call one of the great threats to our society. Countless diet books and programs promise to help us get thin because our lives depend on it.

The government joins in, too. Just two weeks ago, the Centers for Disease Control and Prevention launched a Web site designed to help small and medium-sized employers devise strategies for helping workers manage their weight. At the end of this month, the CDC will convene its first "Weight of the Nation" conference in Washington to discuss obesity prevention and control.

But what if it turns out being fat's not so bad after all?

Late last month, the journal Obesity published two studies that showed overweight and obese people can expect to live at least as long as people of "normal" weight, while underweight folks are at increased risk of premature death.

In one, a survey over 11 years of nearly 27,000 Japanese men and women ages 61 to 79, underweight people and those at the low end of the normal weight range had a greater risk of death than those squarely in the normal range, while neither overweight nor obesity was found to elevate risk of death.

In the other, a Canadian study involving more than 11,000 people ages 25 and older that aimed to pin down the relationship between overweight and mortality, underweight people were at far greater risk of dying during the 12-year study period than those of normal weight, while those who were overweight and obese were at far less risk of dying. Only the very most obese were at increased risk of death.

Though these findings might sound surprising, they are in keeping with those of earlier research, including studies published in the Journal of the American Medical Association in 2005 and 2007.

So why is it so hard to believe, even in the face of such evidence, that being fat's not exactly a death sentence?

Morgan Downey, policy director for the Stop Obesity Alliance, a nonprofit headquartered at George Washington University, also notes that obesity research is complicated by an array of confounding circumstances such as age, ethnicity, sex and lifestyle, which make it hard to establish clear cause-and-effect relationships between poundage and health. Researchers are even scrutinizing the body-mass index, or BMI, the commonly accepted base for defining weight categories, from underweight to morbidly obese.

The BMI, developed in 19th-century Europe and based on a mostly Caucasian population, may not be a reliable indicator of body-fat levels for blacks and Hispanics, for one thing. For another, scientists analyzing data don't always agree as to the exact point at which weight becomes tied to mortality.

Downey points out that, paradoxically, obesity/mortality study results might be skewed by the medical community's focus on treating conditions associated with overweight: For example, he'd be interested in seeing a study in which no participants were on statins (cholesterol-reducing drugs).

And he, like other experts, is certain that obesity contributes to poor health, even if it doesn't kill you.

"The pathway seems clear," he says. "Excess adipose tissue leads to impaired glucose tolerance, which leads to insulin resistance." That sets the stage for metabolic syndrome, he says, which is associated with both cardiovascular disease and Type 2 diabetes.

"A lot of people want to think that [obesity's] not as serious as health officials believe," he says, "and they flock to studies that show overweight is moderately protective. I think there's a little denial going on there."

But Linda Bacon, author of "Health at Every Size," thinks the denial's all on the other side. "It is certainly true that people who are heavier are prone to certain diseases, including Type 2 diabetes," she says. "But just because that's true doesn't mean the fat's to blame."

Perhaps, Bacon notes, a lack of exercise among heavy people, not the extra pounds they carry, is what leads to diabetes. Or perhaps it's something about the food they eat or the way they eat it. "There are so many confounding factors," she says.

That may sound like splitting hairs. But Bacon insists that parsing out these relationships is essential. "The reason this issue is so important is that when we address it as a weight-loss issue, we can't tackle the problem. We don't know any method that really helps people lose weight. And weight loss doesn't get rid of the symptoms [of disease]," she adds. "Changed behaviors are what help reverse disease."

Bacon suggests society should help ensure that people be as healthy as they can by encouraging healthful eating and physical activity habits that don't have weight loss as a goal. Bacon believes that "the body will take care of itself" if people learn to eat when hungry and stop when they're full, to enjoy their foods with gusto, and to engage in physical activity for its own sake.

"People do crazy things to lose weight, and then they just give up," Bacon says. In her 2008 book, she wrotes that she struggled with her weight for much of her life -- until she decided to stop dieting and exercising for weight loss once and for all. She reported that she lost 30 pounds after she stopped obsessing over her weight. While she says she no longer focuses on the number on the scale, photos show her to be quite trim.

I like Bacon's approach. In my lifelong struggle to fit into my jeans, I've noticed that I've done best when I've paid least attention to losing pounds. Getting caught up in a work project, preparing for a special vacation or just concentrating on enjoying life takes my mind off dieting and puts food in proper perspective. Maybe if we as a society could shift our focus away from fighting fat and toward healthier behaviors for their own sake, we'd all be better off.

But I don't see that shift happening any time soon.

Check out Tuesday's Checkup blog post, in which Jennifer challenges readers -- and herself -- to go a whole day without thinking about their weight. Subscribe to the Lean & Fit newsletter by going to http://www.washingtonpost.comand searching for "newsletters." And e-mail your thoughts to Jennifer at checkup@ washpost.com.